Clark W. Perry

[6] The preparation of l-ascorbic acid [35S]2-sulfate having a high specific activity

Publisher Summary The preparation of tracer levels of ascorbic acid [35S]2-sulfate generally involves the treatment of a 5,6-acetal of L-ascorbic acid with an amine-sulfur trioxide complex in a polar aprotic solvent. This chapter discusses the preparation of L-ascorbic acid [35S]2-sulfate having a high specific activity. The sulfation of 5,6-O-isopropylidene ascorbic acid (III) can be carried out more efficiently with sulfur trioxide in dimethylformamide. Removal of the 5,6-isopropylidene group is effected by passage of the labeled substrate (IV) through a column of Dowex 50 (H+) ion-exchange resin, a method that minimizes contamination of the product with inorganic sulfate. The resulting ascorbic acid [35S]2-sulfate can be crystallized as the dipotassium salt or as the barium salt; the insolubility of barium sulfate in water makes purification in this latter case much easier.